Patent GB-776703-A (GB)
Title: Improvements in or relating to electrical potentiometers, variable resistances and the like
Inventor: MASTROPOLE ALFRED JOSEPH
IPC: H01C10/24
Filed: 1955-06-01
Abstract: 776,703. Potentiometers. GIANNINI & CO., Inc., G. M. June 1, 1955, No. 15769/55. Class 37. A potentiometer similar to that described in Specification 760,900 comprises a resistance wire wound helically about a cylindrical insulating support and a brush member extending in a direction parallel to the axis of the support or capable of motion in a direction parallel to said axis, one turn of the helical winding being looped over the brush member to make contact therewith and the brush member being carried by a control shaft extending along the axis of the support, so that on rotation of the control shaft the brush member moves around the support thus varying the point at which it makes contact with the resistance wire. As shown in Fig. 2, the resistance winding is carried on a drum 40 which is provided with a helical thread in which the turns of the resistance wire are located. A control shaft passes axially through the drum 40 and carries at its inner end a plate 82 which rotates with the shaft 30 and upon which is mounted a brush member 87 comprising a strip of resilient conducting material. A portion of the strip is turned down to lie parallel to the surface of the drum and one turn of the resistance wire passes over the turned portion to make contact with the brush member. The other end of the brush member is in resilient contact with a terminal 90. The ends of the resistance wire wound about the drum 40 are connected to rotatable studs, Fig. 3 (not shown), let into the body of the drum 40, whereby the tension in the winding may be varied, and further connecting wires connected to the studs are taken to terminal posts of which one, 77, is shown in Fig. 2. Rotation of the brush member is limited to within a predetermined range by means of nuts 102, 103 arranged on a threaded portion of the control shaft 30 but prevented from rotation therewith by means of projecting portions which engage in a slot 106 formed on the inner surface of the cylindrical support. Stop members 110, 111 formed on the surfaces of the nuts 102, 103, engage with projections 108, 109 attached to the control shaft and thereby prevent rotation of the shaft in excess of a predetermined amount. In a second embodiment, Fig. 6 (not shown), the brush member is arranged to move along the length of the drum as well as about it when the control shaft is rotated, so that the point of contact between the resistance wire and the brush remains at a fixed point on the brush. In this embodiment a single nut having projections extending from opposite surfaces thereof is mounted upon the threaded portion of the control shaft to limit the rotation of the shaft to within a predetermined amount; this nut also serves to carry the brush support member in an axial direction as the shaft is rotated. Fig. 8 shows a modification of the brush member comprising a relatively rigid slotted portion 170 within which slides the brush proper 160, - the brush 160 being shaped to fit within the helical channel formed upon the drum 40 and carry one turn of the resistance wire within a U-shaped recess formed therein. Upon rotation of the control shaft the member 170 rotates about the surface of the drum 40 carrying the brush 160 with it so that the brush progresses in a helical fashion along the resistance wire.